drm/i915: Program BXT_CDCLK_CD2X_PIPE

BXT could change the CD2X divider synchronized with a single pipe.
So assuming the DE PLL frequency doesn't need to be changed, we could
change cdclk without shutting off the pipe (when only a single pipe is
enabled). In the meantime let's configure CDCLK_CTL for non-double
buffered CD2X update, although it shouldn't really matter as long as
the selected pipe is disabled when reprogramming the divider.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1462995892-32416-13-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Imre Deak <imre.deak@intel.com>

drivers/gpu/drm/i915/i915_reg.h

@@ -7566,14 +7566,15 @@ enum skl_disp_power_wells {
 #define  CDCLK_FREQ_540			(1<<26)
 #define  CDCLK_FREQ_337_308		(2<<26)
 #define  CDCLK_FREQ_675_617		(3<<26)
-#define  CDCLK_FREQ_DECIMAL_MASK	(0x7ff)
-
 #define  BXT_CDCLK_CD2X_DIV_SEL_MASK	(3<<22)
 #define  BXT_CDCLK_CD2X_DIV_SEL_1	(0<<22)
 #define  BXT_CDCLK_CD2X_DIV_SEL_1_5	(1<<22)
 #define  BXT_CDCLK_CD2X_DIV_SEL_2	(2<<22)
 #define  BXT_CDCLK_CD2X_DIV_SEL_4	(3<<22)
+#define  BXT_CDCLK_CD2X_PIPE(pipe)	((pipe)<<20)
+#define  BXT_CDCLK_CD2X_PIPE_NONE	BXT_CDCLK_CD2X_PIPE(3)
 #define  BXT_CDCLK_SSA_PRECHARGE_ENABLE	(1<<16)
+#define  CDCLK_FREQ_DECIMAL_MASK	(0x7ff)
 
 /* LCPLL_CTL */
 #define LCPLL1_CTL		_MMIO(0x46010)

drivers/gpu/drm/i915/intel_display.c

@@ -5430,6 +5430,11 @@ static void broxton_set_cdclk(struct drm_i915_private *dev_priv, int cdclk)
 			DRM_ERROR("timeout waiting for DE PLL lock\n");
 
 		val = I915_READ(CDCLK_CTL);
+		/*
+		 * FIXME if only the cd2x divider needs changing, it could be done
+		 * without shutting off the pipe (if only one pipe is active).
+		 */
+		val |= BXT_CDCLK_CD2X_PIPE_NONE;
 		val &= ~BXT_CDCLK_CD2X_DIV_SEL_MASK;
 		val |= divider;
 		/*